1. Field of the Invention
The present invention relates to a spray pack for use in forming a uniform, stable spray coating, comprising a spray container device and, packed therein, a spraying composition comprising a liquid dispersion medium and, dispersed therein, particulate cellulose having an average degree of polymerization (DP) of not more than 300 and an average particle diameter of not more than 10 μm, wherein the spraying composition has a cellulose content of from 0.1 to 5.0% by weight, and wherein the spraying composition exhibits a maximum viscosity value (ηmax) of 1×103 mPa·s or more in the viscosity-shear stress curve obtained, with respect to the composition, using a cone-plate type rotating viscometer in a shear rate region of from 1×10−3 s−1 to 1×102 s−1 and at 25° C. The spraying composition used in the spray pack of the present invention is advantageous not only in that it has excellent spraying properties and also in that, after the spraying, the sprayed composition (coating) has excellent properties with respect to fixation to the surface coated, anti-dripping properties, spreadability and finish (uniformity of the coating). Therefore, the present invention is also concerned with a method for forming a uniform, stable spray coating, which comprises providing a spray pack comprising a spray container device and, packed therein, a spraying composition of the above-mentioned type; and actuating the spray container device to spray the spraying composition onto a surface, thereby forming a spray coating on the surface.
2. Prior Art
In recent years, spraying products are used in a wide variety of fields, such as the fields of skincare products, hair care products, a medicine for external use, a medicine for oral use, an insecticide, a fragrance, a deodorizer, an antimicrobial agent, a sterilizer, a halitosis deodorizer, a detergent, a paint, a coating agent for anti-fogging treatment, a coating agent for anti-static treatment, and an antiseptic agent. A spraying product comprises a spray container device and, packed therein, a spraying composition. In most cases, the spraying composition packed in the spray container device is in liquid form.
A spraying composition is desired to have the following properties: (1) a general purpose container can be used as the spray container device therefor, and good spraying can be performed in a wide variety of environments; (2) after the spraying, the sprayed composition has excellent properties with respect to fixation to the surface coated and the uniformity of the coating; (3) the sprayed composition is unlikely to drip even when the surface coated is vertical or inclined; and (4) when the sprayed composition is dried, a coating can be formed which is not only stable but also has high safety in that skin stimulation (i.e., skin irritation) and the like are not exhibited. However, there is no conventional spraying composition possessing all of these desired properties.
In order to solve the problems of the conventional spraying compositions, various proposals have been made.
For example, in order to solve the tasks (1) to (3) above, Unexamined Japanese Patent Application Laid-Open Specification No. 2001-89359 proposes a method in which a polymeric thickening agent is added to a spraying composition, thereby increasing the viscosity of the composition. However, the following should be noted. In the case of a conventional polymer solution as a spraying composition, when the viscosity of the spraying composition is increased too much by adding a thickening agent in an attempt to prevent the dripping thereof after the spraying, it becomes impossible to spray the composition due to the high viscosity of the composition. Therefore, for enabling drawing up of the composition by suction through the suction tube to the spray nozzle and enabling the spraying of the composition, it is necessary to decrease the viscosity of the composition by some degree. However, such decrease in viscosity, in turn, results in a lowering of the anti-dripping properties of the composition. Therefore, it is very difficult to achieve a good balance of the anti-dripping properties and the sprayability (spraying properties) of the composition. Further, even if conditions can be found which enable the spraying of the composition, there has conventionally been a problem in that, due to the stringiness of the composition (characteristic of a polymer solution), the composition upon being sprayed cannot form desired fine particles (mist); that is, the mist-forming ability of the composition is poor, resulting in non-uniformity of the coating obtained, as compared to the case of a spraying composition which does not contain a thickening agent.
Further, in order to solve the tasks (2) and (3) above, many methods have been proposed, for example, a method in which a surfactant is added to the composition so as to increase the viscosity by utilizing the interactions between the micelles formed in the aqueous phase, and a method in which the surface tension of the sprayed composition (liquid particles) on the coated surface is controlled (see, for example, Unexamined Japanese Patent Application Laid-Open Specification Nos. 2001-72999 and 2000-351726). However, there is a problem, for example, in that the compositions of these patent documents have a fluidity and therefore cannot be sprayed when the spray container device containing such a composition is held upside down. Therefore, the task (1) above cannot be completely solved by these conventional methods. Further, there are other problems, as follows. These conventional methods cannot increase the viscosity of the composition to a level sufficient for substantially completely preventing the dripping after spraying. Furthermore, when a large amount of a surfactant is added to the composition in an attempt to increase the viscosity thereof, the surfactant is likely to irritate the skin. Thus, the task (4) above (concerning safety) and the like cannot be solved.
In order to solve the tasks (1) and (3) above, improvements in the structure of the spray container device have been suggested (see, for example, Unexamined Japanese Patent Application Laid-Open Specification No. 2000-229255). However, this technique poses the following problems. In the case of the use of such a spray container device, when the spraying is performed for forming a thin coating, the dripping after spraying can be prevented. However, when the spraying is performed for forming a thick coating (i.e., when repeated sprayings are needed), there is a problem in that the dripping of the sprayed composition occurs. In addition, in this technique, the spray container device has a complicated structure, so that such spray container device lacks the general-purpose properties and the cost for producing the spray container device becomes markedly high. Therefore, from the viewpoint of developing a spraying composition which can be used without limitation in a wide variety of application fields, this technique cannot be considered as a fundamental solution to the problem of the dripping after spraying.
In an attempt to provide a relatively well-balanced solution to all of the tasks (1) to (4) above, Unexamined Japanese Patent Application Laid-Open Specification Nos. Hei 9-241115 and 2000-51682 disclose a gel-like, spraying composition which contains, as a main component, hectorite comprising hydrophilic smectite. However, the main component of the spraying composition is an inorganic compound which has not actually been put to use for a time long enough to confirm its safety. Further, in the case of this composition, a problem arises in that aggregation of hectorite is likely to occur in a dispersion medium (such as alcohol) which is widely used in a spraying composition, thus causing a lowering of the spraying properties. In addition, there is a problem in that dissolution-out of a large amount of salt contained in hectorite occurs, and the salt is likely to induce aggregation of other components which are sensitive to the presence of salt; this means that the freedom of formulation of the spraying composition is limited.
At the “Dai 13-kai Kobunshi Geru Kenkyu Toronkai (13th Forum on Polymer Gel)” (sponsored by the Society of Polymer Science, Japan; Jan. 17–18, 2002; pages 49–50 of the preliminary text), the present inventors reported their finding that, although an aqueous dispersion of the cellulose used in the present invention has gel-like properties (exhibiting no fluidity), it has excellent spraying properties such that it can be easily sprayed using an ordinary spray container device, thereby exhibiting good spraying. However, for utilizing such finding in a wide variety of fields of industry, it was needed to find conditions under which the gel-like, cellulose dispersion can, as well, exhibit excellent properties with respect to stability of gel and to spraying performance even when the cellulose dispersion is a composite formulation additionally containing not only an alcohol but also various types of additives.